I want to upgrade for have better=] I hear on YOUTUBE a samples of GT10 and i liked it, but i can't judge by a movie, and for this reason I am asking help to know if the difference between the 8 and 10 is honest to upgrade, and if it's a big difference, what is it...

I've used the GT10. It's been changed quite a lot from the GT8, with a bigger screen and a simpler control system. It's also easier to edit and use the pedals, and it has some really neat effects. However, like all effects, there are a lot you would have to wonder where you would use them. I think, if you can use the GT8 well enough, the GT10 isn't really worth the upgrade, at least not yet. Wait until the price drops (it's pretty expensive for a multi-effects unit), then consider getting one.